1. In a large mixing bowl, combine warm milk, melted butter, sugar, and yeast. Let it sit for 5 minutes until frothy.
2. Add mashed sweet potatoes and salt to the mixture. Mix well.
3. Gradually add flour, one cup at a time, until a soft dough forms.
4. Knead the dough on a floured surface for about 10 minutes until smooth and elastic.
5. Place the dough in a greased bowl, cover, and let it rise in a warm place for about 1 hour or until doubled in size.
6. Punch down the dough and divide it into 12 equal pieces. Shape each piece into a roll and place on a greased baking sheet.
7. Cover the rolls and let them rise for another 30 minutes.
8. Preheat the oven to 375°F (190°C). Bake the rolls for 20-25 minutes or until golden brown.
9. Remove from oven and let cool slightly before serving.